Along with development of rural economy and improvement of the agricultural science and technology, the input of chemical fertilizers in agricultural production increases constantly. Among these fertilizers, nitrogenous fertilizer, especially urea is applied increasingly year by year, and urea has gained the well deserved title “dominant fertilizer”, and is becoming one of the important factors affecting the food safety.
The increasing usage amount of urea also stimulates the pursuit of the production scale and yield of urea in the industry. China, for instance, has an annual output of urea of about 70 million tons, making up about 30% of the total output in the world, and the total production and consumption both firmly occupy the first place in the world. With the increasing of the production and application scale, another problem is that the nitrogen use efficiency is poor, or rather, the waste thereof is quite astonishing, it is manifested that the effective nitrogen in the applied urea fails to be absorbed and utilized effectively by the soils and the crops, and the usage effect can be achieved only by increasing the usage amount. Poor utilization rate of fertilizer not only results in a huge waste of energy and a heavy agricultural production burden, the abundant nitrogen loss in the applied urea can also easily cause nitrate nitrogen pollution to the underground water and create the greenhouse effect by the volatilization of nitrogen oxides. How to improve the utilization rate of nitrogen fertilizer especially urea in the agricultural production has become one of the important issues in the fields of agriculture, science and technology, and environmental protection etc. Besides the traditional means such as tillage measures and technique of fertilization, through which the utilization rate of urea could be improved, the research, development and promotion of novel urea products featured by long-term slow-release and high utilization rate have become the important innovative means, and gained widely attention.
From published research literature and patented technology, the means and relevant products for solving long-term slow-release effect of urea are mainly classified into four categories: (1) Products formed by adding in the urea a urease inhibitor for inhibiting urea ammonification or a nitrification inhibitor for inhibiting nitrification or nitrosification of ammonia; (2) coated urea formed by applying a coating to the surface of urea particles to form an insoluble coating structure, and to control the release of nitrogen through permeability of the coating, the common means are to utilize polymer coated urea particles and sulfur coated urea to regulate the release rate and release amount of nitrogen by changing the coating thickness; (3) manufacture of pure slow-release urea products of large particles; (4) synergistic urea products formed by adding polyaspartic acid (salt) with a nature of plant nutrient accelerator into the urea, which can inhibit rapid decomposition and loss of urea composition while accelerating crop absorption.
For the above illustrated urea provided in the prior art, the common point lies in the pursuit of slowing down the water dissolution rate of urea in the soil and achieving the purpose of slow release of urea, or slowing down decomposition of urea by means of urease inhibitor or a nitrification inhibitor.
The prior patent CN 200710121488.3 of the inventor of the present application, entitled “a plant nutrient absorption accelerator and preparation method and application thereof”, discloses a polyaspartic acid chelated potassium (also referred to as “polypeptide chelated potassium”), as a plant nutrient absorption accelerator, it can enrich nutrients and intensify roots of the crop to enable the roots to have a stronger nutrient absorption capability and achieve the purpose of improving nitrogen use efficiency, such that crop can effectively absorb nutrients in a relatively low nutrient environment. The content of CN 200710121488.3 is herein incorporated by reference in its entirety. Based on this and in accordance with the balanced fertilization theory, the inventor proposed upon research that, trace elements can be further properly introduced to provide a synergistic urea containing certain trace element, which can effectively achieve and accelerate the absorption of plant to the nutrients and trace elements, and also help to improve urea use efficiency.
Different soil environment, different crops and different growth periods of the same crop have different demands on trace elements. Boron, one of the seven trace nutrients necessary for the growth and development of plants, mainly acts as a plant growth regulator to be applied to deal with boron deficiency symptom of plants, the influence of boron deficiency on plants is known. The main physiology function of boron in the process of growing a plant can be summarized as: to accelerate the operation of carbohydrates, accelerate a smooth and high quality pollination of plant, regulate the formation and operation of the organic acid in plant. The function of boron is also manifested in enhancing drought resistance and disease resistance and effect on accelerating ripening of crops.
There are two types of application methods of boron fertilizer: in one application method, the boron fertilizer is used as a base fertilizer with an application amount of 7.5-10 kg/ha, and in the other application method, the boron fertilizer is applied as a spray, in which the fertilizer is made into a 1-2% solution and applied once or twice prior to blossom or fruiting. The boron fertilizers currently used are mostly solid fertilizers, usually borax, which is an inorganic boron fertilizer and affected by the solubility. The main problems when applied directly are that, it is very difficult to uniformly disperse the boron fertilizer in the soil, and easy to cause excessive high local boron concentration in the soil, not only poisoning the crops, but also damaging soil quality due to boron residue. Consequently, the current research on boron fertilizer is mainly focused on improving the solubility of boron fertilizer in cold water and the boron content in the boron fertilizer, for example, a modified boron fertilizer by appropriate molecular modification has been provided. However, since the researched boron fertilizer is still mainly in the form of inorganic salts of boron, the aforementioned problems still exist. Therefore, for the applied boron fertilizers, how to ensure uniform boron dispersion, improve the use efficiency of boron element and achieve boron supplement and improve effective absorption capability of crops to boron element are also important issues in boron fertilizer application.